Exploring a museum on the planet Xeros, the travellers discover they are invisible. The Doctor deduces that the TARDIS has jumped a time track and can see their own future.
Back on the proper time track, the travellers take steps to change the future. A rebel force of native Xerons are plotting against the invading Moroks who have captured the Doctor.
After forcing Lobos to revive the Doctor, Ian is also taken prisoner. The Xeron rebellion is underway whilst the fate of the Doctor and his friends still hangs in the balance.
As events escalate, the travellers fear that they will not be able to escape their fate. Vicki helps orchestrate a raid on the Moroks' armoury. Ian attempts to rescue the Doctor.